1. Field of the Invention
The present invention relates to a method of manufacturing an epitaxial wafer having an epitaxial growth layer on a silicon-based substrate and a silicon-based substrate used for the method of manufacturing the epitaxial wafer.
2. Description of the Related Art
To manufacture a semiconductor epitaxial wafer, epitaxial growth is performed on a surface of a silicon-based substrate (such as, for example, a silicon substrate and a silicon carbide substrate), or the like, using a commercially available epitaxial manufacturing apparatus so that a hetero homoepitaxial wafer is manufactured.
In an epitaxial wafer in which an epitaxial growth layer composed of a nitride semiconductor is disposed on a silicon-based substrate, a film thickness of the epitaxial growth layer becomes thicker in an outer peripheral portion, which generates a crown in the epitaxial growth layer (a projection which is higher than a main surface of the epitaxial growth layer).
In order to make warpage of the silicon-based substrate and stress of the epitaxial growth layer optimal at a wafer central portion which is used as a semiconductor device, conditions for a thickness, or the like, of each layer of the epitaxial growth layers are selected. Therefore, if the crown is generated, balance between stress applied to the epitaxial growth layer and warpage of the substrate is lost, which affects the epitaxial growth layer, and generates a honeycomb crack, or the like, in the epitaxial growth layer in the vicinity of the outer peripheral portion (see, for example, FIG. 4).
To prevent generation of such a crown, a method has been proposed which chamfers the outer peripheral portion of the silicon-based substrate and forms an epitaxial growth layer thereon (for example, Patent Literature 1).
Further, as a countermeasure for a crack, there have been proposed to perform epitaxial growth after roughening the vicinity of an Si substrate edge (Patent Literature 2), to use a silicon substrate as a substrate for hetero epitaxial growth, the silicon substrate having as a main surface a (111) plane having orientation flat in a direction obtained by rotating a <110> direction counterclockwise by any angle of 30°, 90° and 150° while using the <111> direction as a rotation axis (Patent Literature 3), or to perform epitaxial growth in a state where a surrounding portion of the silicon-based substrate is covered with a ring (Patent Literature 4).
Further, in an epitaxial wafer in which a GaN layer or an AlN layer is epitaxially grown on a silicon substrate, when a crack is generated at a wafer end portion during epitaxial growth, gas of TMA (trimethyl aluminum) or TMG (trimethyl gallium) which is a material intrudes from space of the crack, reacts with Si and generates a reaction mark.
As a countermeasure for such a reaction mark, it has been proposed to epitaxially grow a thick GaN film via a buffer film (AlN film) on an SOI substrate (Patent Literature 5).